An image recording material containing a developer of a leuco dye has been used in various image recording processes. In the processes, a color image is formed on the image recording material by a reaction of a leuco dye with a developer.
The image recording processes using the leuco dye and the developer can be classified into a light-sensitive process (employing a photopolymerization initiator or silver halide as a photosensor), a pressure-sensitive process and a heat-sensitive process.
The light-sensitive image forming process employing a photopolymerization initiator as a photosensor is described in Japanese Patent Publication No. 64(1989)-7377 and U.S. Pat. No. 4,399,209. The light-sensitive process employing silver halide is disclosed in Japanese Patent Provisional Publication No. 61(1986)-275742 (corresponding to U.S. Pat. No. 4,912,011). The pressure-sensitive process is well known, and is employed in a conventional carbonless copy paper. The heat-sensitive process is also well known as a heat-sensitive copying process.
From another point of view, the image recording processes can be classified into two embodiments. One embodiment employs two sheets which contain the leuco dye and the developer respectively. The other embodiment employs one sheet which contains both of the leuco dye and the developer.
In the former embodiment, a color image is formed on an image recording material by imagewise transferring a leuco dye from an image forming material (such as a light-sensitive, pressure-sensitive or heat-sensitive material) containing the leuco dye to the image recording material.
In the latter embodiment, a color image is formed on an image recording material (which itself is light-sensitive, pressure-sensitive or heat-sensitive) by an imagewise reaction of a leuco dye with a developer in the image recording material.
As the developer of a leuco dye, a salicylic acid derivative or its metal salt has been frequently used. A typical and excellent developer is zinc 3,5-di-.alpha.-methylbenzylsalicylate shown below. ##STR2##
The other salicylic acid developers are disclosed in Japanese Patent Publication No. 52(1977)-1327 and U.S. Pat. Nos. 3,864,146, No. 3,871,900, No. 3,896,255, No. 3,900,215, No. 3,924,027, No. 3,934,070, No. 3,983,292 and No. 4,046,941.